For succesful simulation of STM, we will need (except the STM code) several files. First of all we'll need the right “Fdata” directory (or the link) at our computation directory. Even this files, we will use:
Let's have a look on them.
This files contains information about Hamiltonian of each atom of the elementary cell of the sample. Their number is the same like the number of atoms in “*.bas” file (which is not necessary here).
Inside this file we have the properties settings of the scanning.
The file contains:
0 ! idos(=1 only DOS, =0 STM calculation, =2 Both)
1 ! TIPOSCAN=(0-scan z,1-scan xy z-const,2-scan constant current) 0 ! ICUTT=1 only a xy line 2 ! MODOSCAN(0=tip orbitals,1=sample orbitals,2=both) 0 ! idenomin(1 with denominators) 0 ! ists (=1 compute the STS curve) 0 ! icoupling (=0 old stuff =1 new with fireball format) 1000000 ! energy window for STM (typically 0.4)
Now the initial energy starts from the exact value, and the energy range are the exact voltage.
TIPOSCAN can take three different values:
• 0 if you want to do a scan in a xy constant height changing the z.
• 1 if you want to do the xy scan in constant height.
• 2 if you want to do the xy scan in constant current.
ICUTT can take two values:
• 0 if you want to do a complete xy scan.
• 1 if you only want the line: (XMIN-XMAX,YMIN-YMAX).
MODO_SCAN can take three different character values.
• Tip: means that you do the trace with tip orbitals.
• Sam: means that you do the trace with sample orbitals.
• Two: means that you do both calculations.
IDENOMIN cat take three different values again:
• 0: means that you do the calculation without multiple scattering effect involved (faster).
At this file there is information about the scanning. The distances are in Angstroms.
2.500 ! TIPHEIGHT initial (zmax of the surface atoms+ztip apex) -0.866025 , 0.866025 , 18 ! xmin,xmax,nscanx 0.000000 , 0.000000 , 18 ! ymin,ymax,nscany 1 ! maximum number of iterations 3 3 ! ncellx, ncelly (number of cells for writing: x means in the direction of the 1st vector, and y means in the direction of the 2nd)
The file contains the k-points which will be used for calculations (for the sampling of the k-space). The format is as following:
2 !number of k-points 1.123456 0.500000 0.000000 0.5 !x,y,z coordinate of the k-point and the statistical weight of this k-point 1.123456 -0.500000 0.000000 0.5
The important thing is, the k-points must be symmetric, it is not possible to use just 1/2 of symmetric points.